1. Field of the Invention
The present invention relates to a TFT substrate for a display apparatus and a manufacturing method of the same.
2. Description of the Related Art
Since an LCD is thinner, lighter, and consumes less power than a CRT, the LCD has been generally used for a flat panel display. The LCD typically comprises an upper substrate on which a common electrode and color filters are formed, a lower substrate on which pixel electrodes and thin film transistors (TFTs) are formed, and liquid crystals injected between the upper and lower substrates.
A driving circuit drives the TFT corresponding to each pixel, thereby causing liquid crystal molecules to change their orientation. Such change in the orientation of the liquid crystal molecules controls the amount of light transmitted from a backlight to the color filters.
The TFT comprises a gate electrode, a source electrode, a drain electrode, and a semiconductor layer forming a channel area. Amorphous silicon or polysilicon are used for the semiconductor layer, and the amorphous silicon has low off current. However, the amorphous silicon has a disadvantage in that it generates a leakage current when it is irradiated by light. The leakage current prohibits a storage capacitor from maintaining required potential, thereby generating a flickering or an afterimage.
To prevent the amorphous silicon from being exposed to light of the backlight, a full island structure has been introduced which is designed to form the amorphous silicon within a gate electrode area (i.e., formed only in an area overlapping the gate electrode). However, such a structure disadvantageously has a low aperture ratio since the aperture ratio decreases as the size of the gate electrode becomes large, and such a structure also causes RC delay since RC delay increases as an area where data wiring and the gate electrode overlap becomes large.